CD-ROM Appendix A, which is a part of the present disclosure, is a computer program listing appendix consisting of five (5) text files. CD-ROM Appendix A includes a software program executable on a controller as described below. The total number of compact disks including duplicates is two. Appendix B, which is part of the present specification, contains a list of the files contained on the compact disk. The attached CD-ROM Appendix A is formatted for an IBM-PC operating a Windows operating system.
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
These and other embodiments are further discussed below.
1. Field of the Invention
The present invention is related to analysis of cables and, in particular, to the location of transformers and faults in a cable.
2. Discussion of Related Art
Location of electrical faults in a cable, particularly an underground power cable, can be particularly problematic. In some areas, the power cable is accessible only at connections with transformers, which can be located in hard to reach areas. For example, transformers may be located in inaccessible back yards. It may, in fact, be dangerous for workers to access transformers in order to isolate sections of cables to locate possible electrical faults.
Generally, faults are located in a power cable by isolating and testing sections of the power cable for the fault. A power cable may include several transformers where cables can be disconnected in order that a fault that occurs between adjacent transformers can be located. In addition to being possibly dangerous for line workers to access individual transformers, it is also time consuming to disconnect the cable from adjacent transformers in order to check the cable between the transformers for faults.
Therefore, there is a need for a system that will locate a fault over a long length of cable which includes multiple transformers and, in particular, locate the particular section between transformers that includes the electrical fault.
In accordance with the present invention, a system for automatically locating transformers is described. A fault, then, can be located between adjacent transformers. A transformer can be located by applying a voltage pulse to the cable and measuring the return, reflected signal as a function of time, which results in a reflected signal trace. Transformers, splices, and faults create changes in the impedance of the cable which will reflect the voltage pulse in predictable ways. In particular, transformers will reflect a percentage of the voltage pulse as the voltage pulse travels past the transformer. Since the amplitude of the voltage pulse decreases exponentially with the distance traveled in the cable, the amplitude of the reflected pulses from various transformers decreases substantially exponentially with the distance to the transformer.
A locator for locating the positions of transformers, then, can include a pulse generator, a detector, and a processor (computer). The pulse generator generates the voltage pulse which travels along the cable. The detector measures the reflected signal from the cable. The processor receives the reflected signal from the cable and acquires a reflected signal trace, which is the compiled reflected signal as a function of time from the generation of the voltage pulse. In some embodiments, the time parameter can be converted to distance along the cable by knowing the pulse velocity in the cable.
In some embodiments, the locator can locate an end-of-cable position by recognizing the reflected pulse from the end of the cable. If the cable is open, then the pulse at the end of the cable is a positive amplitude pulse and therefore can be located by searching for the positive pulse with the largest amplitude. In some embodiments, the operator can determine whether the end of the cable has actually been located or not by the locator. A gain can be set by adjusting the reflected pulse from the end of the cable to be above a threshold value. In some embodiments, a distance dependent gain can be determined. The gain is output to the detector which receives the reflected signals from the cable and amplifies them. Further, the operator can locate a range of the reflected signal trace in which to search for transformers and cable faults.
Once the gain is set, then a reflected signal trace can be acquired with the set gain. In some embodiments, the operator can adjust the search range of the reflected signal trace. In some embodiments, the reflected signal trace may be data averaged over several voltage pulses. In some embodiments, the reflected signal trace can be digitally high-pass filtered to remove any offsets which may occur. Further, in embodiments with a distance-dependent gain, the reflected signal trace can be adjusted to counteract for the effects of the gain at the detector.
The locator, then, can find the reflected pulses on the reflected signal pulse that corresponds to the transformers on the cable. In some embodiments, the locator first finds the most negative peak and the next most negative peak. The most negative peak correlates with the position of a first transformer (i.e., the transformer closest to the locator) and the next most negative peak correlates with the position of the second transformer. The locator can then fit an attenuation curve with the amplitude and position of the most negative peak and the amplitude and position of the next most negative peak. A third peak can then be located by finding the next peak with an amplitude and position which substantially adheres to the attenuation curve. In some embodiments, the first peak and the next peak can be utilized to calculate a new attenuation curve. In some embodiments, all of the peaks are utilized to calculate the attenuation curve. Further peaks can then be found by locating peaks that fall on the attenuation curves calculated.
Once the location of each transformer on the cable is located, a high voltage can be applied to the cable. The high voltage causes dielectric breakdown at the fault, causing the fault to act as a short to the voltage pulse. Therefore, a voltage pulse applied to the cable will locate the fault in the cable. The fault, then, is located between adjacent transformers which have already been located.
Once the fault is isolated between two adjacent transformers, the line worker can go to the identified section of the cable and, in some cases, perform a fault location procedure on the isolated cable segment. The cable, then, can be exposed and repaired.
These and other embodiments of the invention are further discussed below with respect to the following figures.